In a conventional spring coupler apparatus 10, as shown in FIGS. 1 and 2, a drive member 11 is provided within a case 14 and a driven member 12 has a projecting portion 12a disposed through a recessed portion 11a formed in the driving member 11. A spring 13 is interposed between the case 14 and the drive member 11 and contacts the inner wall of the case 14 by frictional force. When the drive member 11 is rotated counterclockwise, as shown, the drive member 11 engages one end 13a of the spring 13, and when the drive member 11 is rotated clockwise, the drive member 11 engages other end 13b of the spring 13. Accordingly, the spring 13 is contacted by engaging the driving member 11 and the contacting relation of the spring 13 with the inner wall of the case 14 is removed. Thus when the drive member 11 is rotated in either direction, the frictional relationship of the spring 13 with the inner wall of the case 14 is broken. Thereafter, the recessed portion 11a of the drive member 11 and the projecting portion 12a of the driven member 12 are engaged by the constriction of the spring 13 and the rotation of the drive member 11 is transmitted to the driven member 12.
When the driven member 12, however, is rotated individually in either the clockwise or counterclockwise direction, the drive member contacts either end portion 13a or 13b of the spring 13. Accordingly, the spring 13 is expanded and the frictional force between the spring 13 and the inner wall of the case 14 is increased and any rotation of the driven member 12 is blocked. That is to say, the rotation of the driven member 12 is not transmitted to the drive member 11 and the driven member 12 stays at its previous position.
In this type of conventional apparatus it is indispensable to have sufficient space between the recessed portion 11a of the drive member 11 and the projecting portion 12a of the driven member 12 in order to release the contact of the spring 13 from the inner wall of the case 14 by contraction of the spring when the drive member contacts one end of the spring. In short, if the space is insufficient, the drive member 11 directly engages the driven member 12 and the diameter of the spring 13 is expanded by the driven member 12. The contact of the spring 13 with the inner wall of the case 14 is therefore not released and the drive member 11 cannot rotate. For this reason the driven member 12 is interposed in the space between the end portions 13a and 13b of the spring 13 and the driven member 12 is required to be tiltably rotated in the recess 11a. This tolerance between the driven member 12 and the drive member 11 causes an up and down looseness of the window glass in a window regulator apparatus and of the seat in a seat height adjusting apparatus, when this type of spring coupler is so used. This not only invites discomfort for passengers but also damages the image of the vehicles as perceived by possible purchasers.